Final Summary

This summer went by fast! I feel I have accomplished a lot!

The goal of my project was to determine if genes required for sexual reproduction are undergoing selection to facilitate speciation in the yeast Saccharomyces paradoxus. Saccharomyces paradoxus is woodland yeast found in Europe and North America. In a previous lab, my advisor found evidence of speciation in this yeast. In a recent migration event, a European Saccharomyces paradoxus population migrated to North America. This Migrant population exhibited mating discrimination towards potential North American mates while its ancestral European populations did not. This behavior likely evolved in the Migrant population to avoid reproducing with genetically incompatible North American potential mates, as the offspring of inter-population pairings were substantially less viable. This served as evidence for speciation.

At the beginning of the session, my lab partner and I tied up some loose ends from our fall and spring semester project. From our results, we concluded that the sexual agglutinin family of genes does evolve at a faster rate than other families of genes.

After this, I began learning the microbiology techniques necessary for me to begin my research project. I started by learning how to perform PCR. In PCR, I amplified the sexual agglutinin genes of interest along with antibiotic resistance genes. After successfully performing PCR, I began my transformations. In the transformations, I inserted the amplified DNA into the yeast genomes. To do this, I had to make the yeast cell walls porous. Next, I inserted the amplified DNA using single stranded carrier DNA. In order to ensure I was working only with yeast that incorporated the DNA I inserted, I plated the yeast on antibiotic plates corresponding to the antibiotic resistance gene that was amplified along with the gene of interest. If yeast incorporated the amplified DNA, it possessed the antibiotic resistance gene and grew on the plates.

Next, I marked the colonies that survived on the antibiotic plates so I could streak them. After letting them grow a bit, I placed the yeast on a low nutrient medium, inducing sporulation. During sporulation, diploid yeast cells undergo meiosis and produce four haploid spores. Two of these spores should have the gene of interest, along with the antibiotic resistance gene while two should not. After allowing the yeast sufficient time to undergo sporulation, I performed a dissection. In a dissection I used a dissection microscope to separate the four spores within the asci, placing them into columns on a normal YPD plate. After letting the yeast grow, I replica plated them, placing them on antibiotic plates corresponding to the antibiotic resistance genes they possessed to determine which spores contained the gene of interest.

This was as far as I got this summer. I plan to continue this research in the next year. During this time, I will perform mate choice trials to determine if swapping the sexual agglutinin alleles among strains of European, North American and Migrant Saccharomyces paradoxus affects mating behaviors. I feel I have learned a lot this summer. I have been able to practice various microbiology and molecular lab techniques. My lab partner and I have also been able to finalize the lab project we were working on the past year. I really enjoyed performing research this summer, and I’m excited to continue in the fall!


  1. This sounds like a really cool project and it was easy to understand for people without science specific backgrounds. Congrats on your work!

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